The main working principle of the microwave oven is to transform the electric energy into high-frequency microwave energy which act on the moisture of the food to generate heating to achieve the cooking object. During the cooking process much moisture of the food will be lost and the food will become hardened. Furthermore, when cooking bulk mass food items, the food often incur a hardened surface yet insufficiently heated interior. To solve this problem, many companies have designed microwave ovens with steam generating system to let the microwave ovens have the function of steam cooking to ensure that the food items maintain enough moisture after being cooked in microwave ovens.
There are two main forms of the steam generating system of the microwave oven in the prior arts. In the first form, such as “the microwave oven with steam generating device” disclosed in the Chinese PAT. No. CN200320118994.4, the main structure of the microwave oven comprises a microwave oven body, a control board and a control circuit, and there are a detachable rack, a water droplet generating mechanism and a steam generating mechanism in the cavity of the microwave oven, the mechanisms being connected to the control circuit, the water droplet from the drip tube dripping on the heating plate to generate steam for cooking, thus ensuring that the food items maintain enough moisture. The heating plate has a heating component inside, and its bottom is attached on the inside surface of the cavity of the microwave oven. As a consequence, the cavity will be distorted after certain time, and the heating plate will accumulate dirt deposit, so the steam generated is not pure.
In the second form, such as “microwave oven with steam cooking function” disclosed in Chinese PAT. NO. CN200320118995.9, the main structure comprises a cavity, a microwave emitting device, wherein the microwave emitting device connected to a control board via a control circuit, further comprises an aluminum shield plate with perforations to shield from the microwave, the shield plate separates the cavity of the microwave oven into two chambers arranged up-down or left-right, but it still comprises a boiler and a steam generating device, the steam generating device and the boiler are mounted in different chamber respectively. The main working principle of the oven is to use the microwave energy to act on the water in the steam generating device to generate high-temperature steam, which will cook the food in the boiler. Because the cavity is separated into two chambers, the space for hold food items to be cooked is reduced. Also, the grease or juice generated by the food drips on the steam generating device to pollute the water there, the steam generated by the polluted water will affect the food safety. Furthermore, because cooking is by steam only, so the cooking process is slow.
Similarly, other food processors such as toasters and grills and so on have the same or similar problems as well.